In the recovery of natural brines, oil, gas and the like from producing wells, a major problem is corrosion of the well casing from attack by constituents in the product. Such attack has been estimated to cause more than 2 billion dollars worth of damage annually. If some method of preventing such damage is not employed, the corrosive effects over a period of time will corrode the well casing. The casing must then be repaired by inserting a liner at the damaged section of casing. Once a liner is installed, smaller production tubing is required. Such procedures are expensive, result in considerable periods of lost production time with the well being out of service and if a liner is set in the casing, the use of smaller equipment for downhole operations is required. Thus, it is desirable to find an efficient and relatively inexpensive means for preventing corrosive attack of extreme service well casing. For example, the formation of a protective passive film of oxides is not possible because of the water and/or hydrocarbon fluids passing through the well which carry off the oxides formed. Thus, the use of film-forming or reactive-type corrosion inhibitors has been found to be the most practical although less than completely satisfactory method of protecting well casing.
In general, use of corrosion inhibitor has involved excessive amounts of material relative to the coating applied, much of which is wasted, and presents problems of contaminating the well product or plant processing equipment. For example, corrosion inhibitor has previously been pumped directly into open well casing, or pumped through the production tubing. Another method of application is to pull the production tubing and run a swab cup, a close fitting solid rubber flange, down the well pouring inhibitor down after it and swabbing down the casing on pulling up the swab cup.
None of the prior art methods described above allow close control over the coating thickness and allow application under controlled conditions. It is believed that the present invention offers advantages of using only enough inhibitor to do the job, application of corrosion inhibitor under controlled conditions and reducing product and process equipment contamination problems.
In accord with the present invention, there is provided an apparatus which allows the application of a relatively uniform coating of corrosion inhibitor to oil, gas, brine and similar wells having corrosion problems which has the advantage of using only enough material to place the desired coating on the well casing and, hence, causes less interference with process control and product contamination.